$ \left(\dfrac{8}{5}\right)^{-3}$
Explanation: $= \left(\dfrac{5}{8}\right)^{3}$ $= \left(\dfrac{5}{8}\right)\cdot\left(\dfrac{5}{8}\right)\cdot \left(\dfrac{5}{8}\right)$ $= \dfrac{25}{64}\cdot\left(\dfrac{5}{8}\right)$ $= \dfrac{125}{512}$